2003-01-24
Power loss in conductors stems from the fact that wire has
resistance. The resistance may be small, but it is still there. The
resistance of copper wire is determined by multiplying the resistivity of the
metal used for the wire (usually copper) by the length of the conductor in
the current path and divided by the cross sectional area of the conductor.
If we take the resistivity and divide it by the cross
sectional area of the conductor (converted to square metres) we can get the
resistance per metre length. In the case of a 1.5 mm^2 size wire, the
resistance is 11.153 mΩ/m.
If the conductor length from the distribution box to the
wall socket and back was equal to 10 m, the total resistance of the wire would
be 112 mΩ. If the current passing through the conductor is 15 A, the total
power loss is 15^2 x .0112 = 25.2 W, or 2.5 W/m. The voltage drop in the
line would be 0.112 x 15 = 1.68 V. On a 120 V circuit, this loss is
minimal. Also, the load would draw 15 x 120 = 1.8 kW. 25.2 W
out of 1.8 kW is not much of a loss.
If the same size wire was used on a 240 V circuit and the
device was designed to use the same power, it would draw half as much
current. In this case, 7.5 A. The loss in the lines would be 7.5^2 x
0.112 = 6.3 W or 0.63 W/m. This is exactly 0.25 of the power lost when the
voltage was 120 V.
This is the point the webpage was trying to get
across.
But, the 4:1 advantage is not wholly realised in countries
where 240 V is standard. One of the reasons most of the world uses 240 V
is because they can use smaller wire due to the lower currents, and thus save on
the cost of copper. An 1.8 kW load can safely run on 1.0 mm^2 instead of
1.5 mm^2. A 10 m length of this size wire would be 167 mΩ instead of 112
mΩ. By doing the math, one can see that the line loss is only about 0.67
instead of 0.25 that one gets if the wire size is kept the same.
I'm sure when Korea changed it's voltage to 240 V from 120
V, they incurred some big time costs. Their thinking was that in the long
term it would pay for itself and save resources and energy which is 100 %
imported. Such a change in the US could be astronomical. The present
wall outlets are not safe at 240 V. Korea had to change them from the US
type to the Schucko type. I don't know if the Korean transformers had dual
120/240 V outputs or not. If they did, then all that had to be done is to
change the taps from 120 V to 240 V. If not, then the whole transformers
had to be changed. If the Edison wire system is to be retained in the US,
then the 240 V line to grounded centre tap would produce 480 V between the two
ends. This may be too high of a voltage to bring into ones
home.
The cost and minimal gain that would be achieved by
switching from 120 to 240 V is not worth the effort. It isn't even a
subject worth discussing.
Copper Properties:
Naturally occurring element
- Atomic Weight 63.546
- Atomic Number 29
- Two isotopes:
- 63 (69.17%)
- 65 (30.83%)
- Crystal Structure: face centred cubic
- Density 89.2 kg/m^3
- Resistivity 1.673^-8 Ω.m
- Thermal conductivity 401 W/m.K
- Molar volume 6.712 cm^3/mole
- Coefficient of Linear Thermal Expansion 16.6^-6 /K
- Molar heat capacity 24.435 J/mol.K
- Melting point 1336.6 K
- Boiling point 2840 K
John
----- Original Message -----
From: "M R" <[EMAIL PROTECTED]>
To: "U.S. Metric Association" <[EMAIL PROTECTED]>
Sent: Friday, 2003-01-24 10:10
Subject: [USMA:24595] Voltage
conversion
> http://www.faqs.org/faqs/electrical-wiring/part2/section-11.html
>
> it says that
> '110 V loses 4 times more power in the house wiring
> than a 220V motor', so all those devices like fans,
> blenders (kitchen mixers), vacuum cleaner,
> driers consume 4 times more power and increases the
> bill unnecessarily for the consumer.
>
> Is it possible for USA to switch over to 220 V in the
> same way as Korea does. May be a Surge Protector with
> an inbuilt transformer to converter to convert 110 V
> -> 220 V should be introduced. Then people will buy
> motors which has 220 V unit.
>
> Madan
>
>
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